It is well known that the emulsion polymerization of fluorinated olefins in the presence of ordinary emulsifiers is very often inhibited or gives at best polymers without interest, as is the case for example with polymers produced with ionic or nonionic surfactants having short hydrocarbon chains substituted on to aromatic rings. Polymers made with such emulsifying agents have in particular a poor thermal stability.
During recent years various perhalogenated emulsifiers have been proposed for the polymerization of fluorinated olefins and in particular the salts of chlorofluorinated or perfluorinated carboxylic acids, of omega-hydrogenated, perfluorinated carboxylic acids, of perfluorinated sulfonic acids, of chlorendic or hexachloroendo-methylene tetrahydrophthalic acids, or of perchlorobenzene mono- or di-carboxylic acids. (U.S. Pat. Nos. 3,245,971 and 3,475,396 for example.)
However, in the case of vinylidene fluoride polymerization the salts of perhalogenated carboxylic acids, which decompose on heating, form colored degradation products and unsightly blisters and also lose strength and other desirable physical properties and lead to polymers of poor thermal stability, at least according to the tests set forth herein. The salts of perfluorinated sulfonic acids which would be satisfactory from that standpoint, are not available on the market in industrial quantities since the delicate method required for their manufacture has made them very costly.